1. Field of the Invention
The invention relates to a light irradiation device for optical alignment of liquid crystals in which an alignment layer of a liquid crystal cell element is irradiated with polarized light.
2. Description of Related Art
A liquid crystal cell element is typically produced as follows:
An alignment layer which has been formed on the surface of a transparent substrate is treated for alignment of the liquid crystal into a desired direction (alignment treatment).
Two of these transparent substrates are cemented to one another such that the alignment layers are located on the inside and between the two substrates and a gap with a stipulated distance is maintained.
Liquid crystals are injected into this gap.
For the above described alignment treatment of the alignment layer of a liquid crystal cell element, there is a technique which is called xe2x80x9coptical alignmentxe2x80x9d. Here an alignment layer is irradiated with polarized light and exposed.
An irradiation device for polarized light for optical alignment is known, for example, from U.S. Pat. No. 5,934,780 which has already been proposed by the present applicant and assigned to the assignee of the present invention.
FIG. 11 shows the arrangement of the above described irradiation device 15 for polarized light which exposes the entire surface of a transparent substrate (hereinafter called the xe2x80x9cworkpiece Wxe2x80x9d) on which an alignment layer is formed. This figure illustrates a discharge lamp 1 such as a super high pressure mercury lamp or the like, an oval focusing mirror 2, a first plane mirror 3, an integrator lens 4, a shutter 5, a second plane mirror 6, and a collimation lens 7 (a collimation mirror can also be used). Here however, a case is described in which a collimation lens is used. The reference number 8 labels a polarization element. In the polarization element 8 there are several glass plates 8a that are parallel to one another and are at a distance from one another. The plates are tilted by the Brewster angle with respect to the parallel light emerging from the collimation lens 7.
In the FIG. 11, the light which is radiated from the discharge lamp 1 and which contains UV radiation is focused by an oval focusing mirror 2, reflected by the first plane mirror 3 and is incident in the integrator lens 4. The light emerging from the integrator lens 4 is furthermore reflected via the shutter 5 by the second plane mirror 6, is converted into parallel light by the collimation lens 7 and is incident in the polarization element 8. Since a polarization element 8 transmits P-polarized light and for the most part, reflects S-polarized light, the light emerging from the polarization element 8 is converted mainly into P-polarized light which is emitted onto the workpiece W, such as a substrate or the like, which has been placed on the workpiece carrier 11. In FIG. 11 there are a mask M and an alignment microscope 10 which are used in the case of exposure by the above described multi domain method.
One liquid crystal cell element which is being currently used especially often (hereinafter called xe2x80x9ca TN liquid crystalxe2x80x9d) is produced in such a way that the alignment direction of the liquid crystal is turned by 90xc2x0 between two transparent substrates. To produce a xe2x80x9cTN liquid crystalxe2x80x9d therefore, two transparent substrates are needed with alignment layers which have different alignment directions.
In the irradiation device 15 shown in FIG. 11 for polarized light for optical alignment, to change the polarization direction of the polarized light which irradiates the alignment layer, conventionally the direction of the workpiece is changed. Afterwards the workpiece is put in place and exposure is done when the workpiece has been placed on the workpiece carrier which is irradiated with polarized light.
For example, in the case of the above described xe2x80x9cTN liquid crystalxe2x80x9d one workpiece is turned with respect to another workpiece by 90xc2x0, placed on the workpiece carrier 11 and irradiated with polarized light.
On the other hand, there is a pixel division method (also called the multi domain method) in which one pixel of a liquid crystal cell element is divided into two or more pixels, the alignment direction of the liquid crystal is changed for the pixel which has been formed by division, and thus, the angle of view field of the liquid crystal cell is improved.
In the case of using optical alignment for this pixel division method, the mask M which is shown in FIG. 11 and the alignment microscope 10 are used. Mask alignment marks and workpiece alignment marks are determined by the alignment microscope 10 and the workpiece carrier 11 is moved in the X-Y-xcex8 directions (X-axis: the axis parallel to the workpiece surface, Y-axis: the axis which orthogonally intersects the X-axis and which is parallel to the workpiece surface, Z axis: the axis which orthogonally intersects the X-Y axes, xcex8: rotation around the Z-axis) to align the mask M to the workpiece W. After the alignment is completed, part of the pixel which has been generated by division and which was formed in the workpiece W is irradiated via the mask M with polarized light (here the mask M is provided with an opening pattern so that a partial area of the above described pixel, besides the part formed by division, is shielded).
Next, the mask M is replaced. The other part of the pixel formed by division is irradiated with light in the same way; the polarization direction of this light differing from the above described polarization direction. Since in the case of the device shown in FIG. 11, the polarization direction of the polarized light which irradiates the respective part of the pixel which has been formed by division is changed, the workpiece W together with the mask M must be turned and moved.
A transparent substrate (workpiece) of a liquid crystal cell element is made rectangular according to the shape of the liquid crystal cell, for example measuring 550xc3x97650 mm or 650xc3x97830 mm. In the irradiation device shown in FIG. 11 for polarized light, the light beam emerging from this device thus, conventionally has a shape which corresponds to the shape of the liquid crystal cell (the integrator lens 4 shapes the light beam). This is because the overall surface of the above described rectangular workpiece W must be completely exposed and the collimation lens 7 and the like of the irradiation device for polarized light is made as small as possible.
But in the case in which the workpiece, after changing its direction, is placed on the workpiece carrier, to change the polarization direction of the polarized light irradiating the alignment layer, it is necessary to make the light beam of the polarized light which irradiates the workpiece, as large as possible according to the longer side of the workpiece.
For example, in the case in which in a workpiece measuring 650xc3x97830 mm the polarization direction of the emitted polarized light is changed by 90xc2x0, it is necessary for the size of the light beam emitted onto the workpiece carrier to be at least 830xc3x97830 mm. This means that the size of the light beam is made larger than the surface of the actually irradiated workpiece. Consequently the light from the light source cannot be efficiently used.
To change the direction of the workpiece and to place it on the workpiece carrier, in a device for transporting the workpiece into/out of the workpiece carrier, there must be in addition (for example) a workpiece rotary part, such as for example a rotary carrier or the like and thus, the workpiece must be turned, or after placing the workpiece on the workpiece carrier the workpiece carrier must be turned.
But if an attempt is made to turn a large workpiece measuring 550xc3x97650 mm or 650xc3x97830 mm using the transport device, a large transport device is needed, with a proportion of the entire device which becomes larger causing the entire irradiation device to become larger. In the case of rotation of the workpiece carrier, a large workpiece carrier is turned. The construction of the device with respect to the competition for space of the above described workpiece transport device, protecting the rotational space and the like are made difficult. Consequently, the entire device also becomes larger.
In the case of use of the pixel division method, both the workpiece and also the mask must be turned. In order to turn the mask, a mask carrier rotation device is needed, causing the entire device to be even larger.
The invention was devised to eliminate the above described deficiency in the prior art. Therefore, the first object of the invention is to devise an irradiation device for polarized light for optical alignment of a liquid crystal cell element in which the polarization direction of the polarized light emitted onto the workpiece can be changed, and the light from the light source can be effectively used without the size of the light beam being made much larger than the area of the workpiece which has actually been irradiated.
A second object of the invention is to devise an irradiation device for polarized light for optical alignment of a liquid crystal cell element which eliminates the requirement for a transport device with a workpiece rotary part and eliminates the need for the workpiece carrier to turn where the entire irradiation device is not made larger, and in which also in an application for the pixel division method the mask need not turn.
These objects are achieved in accordance with one embodiment of the present invention by providing an improved irradiation device for polarized light for optical alignment of a liquid crystal cell element which comprises a lamp, a focusing mirror for focusing of the light of the lamp, an integrator lens, and a polarization element where the polarization element is made such that several glass plates which are located parallel to one another at a distance are tilted by the Brewster angle with reference to the optical axis. In accordance with the present invention, the rotary motion of the above described polarization element around the center of the light beam incident in the polarization element (light beam being the axis of rotation), changes the polarization direction of the polarized light with which the alignment layer of the liquid crystal cell element is irradiated.
In accordance with another embodiment, the polarization element may be located in the vicinity of the integrator lens. In addition, the polarization element may be made in such a way that several glass plates which are located parallel and at a distance to one another and which are tilted by the Brewster angle with reference to the optical axis of the incident light beam, are each combined with one another in a V-shape and their apex lines pass through the center of the light beam. In another embodiment, the above described two groups of the polarization elements may be arranged so that the directions of the apex lines of their V-shapes agree with one another and the directions of the V-shapes differ from one another. In yet another embodiment of the polarization element of the irradiation device for polarized light for optical alignment, the connecting surface of the two glass plates may be in contact with a plane in which the angle of incidence (with reference to the optical axis of the light incident in the polarization element) is 90xc2x0.
The preferred embodiments of the present invention are set forth in detail below together with the attached drawings.